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Abstract

Background

Several studies showed that blood pressure and lung function are associated. Additionally,
a potential effect of antihypertensive medication, especially beta-blockers, on lung
function has been discussed. However, side effects of beta-blockers have been investigated
mainly in patients with already reduced lung function. Thus, aim of this analysis
is to determine whether hypertension and antihypertensive medication have an adverse
effect on lung function in a general adult population.

Methods

Within the population-based KORA F4 study 1319 adults aged 40-65 years performed lung
function tests and blood pressure measurements. Additionally, information on anthropometric
measurements, medical history and use of antihypertensive medication was available.
Multivariable regression models were applied to study the association between blood
pressure, antihypertensive medication and lung function.

Results

High blood pressure as well as antihypertensive medication were associated with lower
forced expiratory volume in one second (p = 0.02 respectively p = 0.05; R2: 0.65) and forced vital capacity values (p = 0.01 respectively p = 0.05, R2: 0.73). Furthermore, a detailed analysis of antihypertensive medication pointed out
that only the use of beta-blockers was associated with reduced lung function, whereas
other antihypertensive medication had no effect on lung function. The adverse effect
of beta-blockers was significant for forced vital capacity (p = 0.04; R2: 0.65), while the association with forced expiratory volume in one second showed
a trend toward significance (p = 0.07; R2: 0.73). In the same model high blood pressure was associated with reduced forced
vital capacity (p = 0.01) and forced expiratory volume in one second (p = 0.03) values,
too.

Conclusion

Our analysis indicates that both high blood pressure and the use of beta-blockers,
but not the use of other antihypertensive medication, are associated with reduced
lung function in a general adult population.

Background

Hypertension is an increasingly important public health challenge worldwide and it
is one of the major causes for morbidity and mortality [1]. Thus, the National High Blood Pressure Education Program reports that the global
burden of hypertension is approximately 1 billion individuals and that more than 7
million deaths per year may be attributable to hypertension [2].

Moreover, hypertension has been linked to multiple other diseases including cardiac,
cerebrovascular, renal and eye diseases [3]. Beside the well-established association between hypertension and vascular comorbidities,
several studies showed that blood pressure and lung function are associated [4-9]. It could be demonstrated that higher forced vital capacity (FVC) is a negative predictor
of developing hypertension [7,8]. Moreover, some studies found an association between reduced pulmonary function,
including both low FVC and low forced expiratory volume in one second (FEV1), and hypertension [5,9,6].

Furthermore, there are a number of publications discussing the controversial effect
of beta-blockers (BBL) on lung function [10-16]. It is well established that BBL, even relatively cardioselective agents, can produce
bronchoconstriction and thereby worsen respiratory flows and symptoms in patients
with asthma or chronic obstructive pulmonary disease (COPD) [10,16,12]. However, two recent studies suggested that the treatment of cardiovascular diseases
with cardioselective BBL, may reduce morbidity and mortality in patients with COPD
[11,15]. Two systematic reviews of randomized controlled trials showed that the use of cardioselective
BBL in patients with asthma or COPD has no adverse effects on lung function or respiratory
symptoms [13,14]. However, these studies investigated the potential effect of BBL intake on lung function
mainly in patients with already existing pulmonary diseases. The association between
blood pressure, antihypertensive drug treatment and limited lung function in a population-based
setting is much less investigated. Thus, the aim of this analysis is to determine
whether hypertension as well as antihypertensive medication has an adverse effect
on lung function in a general adult population.

Methods

Study population

The KORA F4 study is a follow-up of the KORA S4 study, a population-based health survey
conducted in the city of Augsburg and two surrounding counties between 1999 and 2001.
A total sample of 6640 subjects was drawn from the target population consisting of
all German residents of the region aged 25 to 74 years.

Of all 4261 participants of the S4 baseline study, 3080 also participated in the 7-year
follow-up F4 study. Persons were considered ineligible for F4 if they had died in
the meantime (n = 176, 4%), lived outside the study region or were completely lost
to follow-up (n = 206, 5%), or had demanded deletion of their address data (n = 12,
0.2%). Of the remaining 3867 eligible persons, 174 could not be contacted, 218 were
unable to come because they were too ill or had no time, and 395 were not willing
to participate in this follow-up, giving a response rate of 79.6%. Our study focuses
on a subset of 1319 persons aged 40-65 years, because only this age-restricted subset
performed both blood pressure measurements and lung function tests. The clinical examinations
and interviews were performed at the same day. Overall, the KORA F4 study was conducted
between 2006 and 2008.

The investigations were carried out in accordance with the Declaration of Helsinki,
including written informed consent of all participants. All study methods were approved
by the ethics committee of the Bavarian Chamber of Physicians, Munich.

Outcome assessment

Lung function

Lung function examinations, i.e. spirometry, were conducted based on the American
Thoracic Society (ATS) criteria [17] and the recommendations of the European Community for Steel and Coal (ECCS) [18]. The participants performed at least three forced expiratory lung function manoeuvres
in order to obtain a minimum of two acceptable and reproducible values. Before the
tests the examiner demonstrated the correct performance of the manoeuvres and then
the individuals were supervised throughout the tests. According to the ATS recommendations
[17] the tests were performed in a sitting position and with wearing noseclips. The best
results for FVC and FEV1 were taken and percent predicted values were calculated according Quanjer et al. [18].

Blood pressure, medication and other determinats

Blood pressure was measured using a validated automatic device (OMRON HEM 705-CP).
Three independent blood pressure measurements were taken with a 3-minute pause after
a rest of at least 5 minutes in a sitting position on the right arm. The mean of the
last two measurements was used for the current analyses. High blood pressure (HBP)
was defined as blood pressure ≥ 140 mm Hg systolic or 90 mm Hg diastolic (with or
without antihypertensive medications). Additionally, anthropometric measurements,
computer-assisted standardized interviews and self-administered questionnaires on
lifestyle and health related factors, medical history and respiratory symptoms were
performed. Cardiovascular (heart attack, stroke) and pulmonary diseases (asthma, chronic
bronchitis) were based on self-reported physician's diagnosis. The smoking status
(current, former, or never-smokers) was assessed by self-report. Education level was
defined by the highest graduation (less than O-level, O-level and more than O-level).
Furthermore, the use of medication within the last seven days before the examination
was ascertained by an instrument for database-assisted online collection of medication
data (IDOM) [19]. The following substance classes were considered as antihypertensive medication according
to the recommendations of the German Hypertension Association [20]: Antihypertensives (ATC code C02), diuretics (ATC code C03), beta-blocker (ATC code
C07), calcium antagonists (ATC code C08), ACE inhibitors and angiotensin antagonists
(ATC code C09). Finally, the following classes of high blood pressure based on the
blood pressure measurement (HBP ≥ 140/90 mmHg) and antihypertensive medication were
defined:

- A. HBP: high blood pressure regardless of its medical treatment

- B. HBP or medication: high blood pressure or the use of antihypertensive medication

- C. HBP and medication: high blood pressure and the use of antihypertensive medication;
treated but uncontrolled hypertension

- D. Only HBP: high blood pressure, but no antihypertensive medication; untreated
hypertension

- E. Only medication for HBP: antihypertensive medication, but no high blood pressure;
treated and controlled hypertension

Statistical analyses

Descriptive analysis for the study population, blood pressure and lung function measures
was done using chi-square and Kruskal Wallis tests to determine significance levels.
Kruskal-Wallis tests and multivariable linear regression models were applied to study
the association between the abovementioned classes of high blood pressure and antihypertensive
medication and lung function outcomes. Additionally, high blood pressure and antihypertensive
medication were used as individual variables in one regression model. P-values < 0.05
were considered statistically significant for all analyses. All statistical analysis
was performed with SAS, version 9.13.

Results

Table 1 shows gender-specific characteristics of the 1319 participants with complete data
on lung function tests and blood pressure measurements. Women had a significantly
lower body mass index (BMI), smoked less and their blood pressure readings and absolute
lung function values were lower, whereas their percent predicted lung function values
were higher compared to men (p < 0.01 for each comparison). Overall high blood pressure
was less prevalent in women compared to men (10.3% versus 23.1%; p < 0.01). However,
for the use of antihypertensive medication there was no difference between women and
men.

Table 1. Characteristics of the study population based on KORA F4, persons aged 40-65 years
with blood pressure measurements and lung function tests

Similar results for the association between high blood pressure, antihypertensive
medication and lung function could be shown in men. In women FEV1 and FVC % predicted values did not differ between subjects with and without high blood
pressure. However, the use of antihypertensive medication irrespective of high blood
pressure was associated with a significant reduced FEV1 and FVC % values in women (p = 0.02 and p < 0.01, respectively).

The descriptive analysis (Table 2) of the association between lung function and antihypertensive medication showed
that both BBL and other antihypertensive medication, as for example ACE inhibitors,
angiotensin antagonists, diuretics or calcium antagonist, are associated with reduced
FEV1 and FVC % predicted values (p = 0.01 and p < 0.01, respectively).

The application of multivariable regression models revealed that high blood pressure
as well as antihypertensive medication are associated with lower FEV1 (p = 0.02 and p = 0.05, respectively) and FVC values (p = 0.01 and p = 0.05, respectively)
after adjusting for sex, age, height, weight, education level, packyears of smoking,
pulmonary and cardiac diseases (Table 3, Model 1 and 3). When using both high blood pressure and antihypertensive medication
as individual variables in one regression model, it could be shown, that both variables
were associated with reduced lung function values (Model 6). However, antihypertensive
medication showed only a trend toward a significant association with lower FEV1 and FVC values (each p = 0.08). Furthermore, the adjusted regression models with mutual
exclusive categories pointed out that the combination of high blood pressure and the
use of antihypertensive medication had the strongest negative effect on lung function
(Model 4). Thus, among treated but not controlled hypertensive subjects FEV1 had a lower volume of 160 mL and FVC of 170 mL compared to subjects with no high blood
pressure and no antihypertensive medication (each p = 0.02 and p = 0.02). A detailed
analysis of antihypertensive medication showed that the use of BBL was associated
with reduced FEV1 and FVC values, whereas other antihypertensive medication had no effect on lung function
(Model 5). However, it has to be considered that the effect of BBL was significant
for FVC (p = 0.03) while for FEV1 the association was of borderline significance (p = 0.07). A further model including
BBL, other antihypertensive medication and high blood pressure showed similar negative
effects of BBL on FVC (p = 0.04) and FEV1 (p = 0.07). Besides, high blood pressure was associated with reduced FVC (p = 0.01)
and FEV1 (p = 0.03) values, too (Model 5a). An additional sensitivity analysis of the models
5 and 6, where we excluded subjects with obstructive lung diseases, showed that the
effect of BBL still exists. Although the significance level declined the magnitude
effect estimates did not change. For all multivariable regression models the adjusted
r-squared value was 0.65 for FEV1 and 0.73 for FVC.

A further sensitivity analysis regarding the possible effect modification by gender
showed no gender difference for FEV1 for all models. The multivariable regression models for FVC, however, showed a significant
interaction between gender and high blood pressure, indicating that high blood pressure
has a lower effect on lung function in women compared to men. Further analyses regarding
the ratio FEV1/FVC showed no significant association between high blood pressure or antihypertensive
medication and the ratio FEV1/FVC.

Discussion

The present analysis of a population-based study demonstrates that both high blood
pressure and the use of BBL are associated with reduced lung function, whereas other
antihypertensive medications have no effect on lung function.

Our findings are in line with previous observations that blood pressure and lung function
are inversely associated [5,6,9]. But most of these studies did not differentiate between the effect of high blood
pressure and the effect of antihypertensive medication on lung function. Instead they
defined hypertension as elevated blood pressure or use of antihypertensive medication.
One study, however, found no difference in FEV1 and FVC between hypertensive subjects that used or did not use beta blocking antihypertensives
[6], but they did not specifically address the effect of antihypertensive medication
independent of high blood pressure on lung function.

Thus, our study might substantially add to the question, whether antihypertensive
BBL medication independent of high blood pressure has adverse effects on lung function.
Beta-adrenergic receptors (β-ARs) play a key role in the regulation of bronchomotor
tone [21]. In the respiratory system most of the β-ARs are β2-ARs. However, there are β1-ARs,
too, which are responsible for the respiratory effects of cardioselective β1-antagonists.
Two systematic reviews suggest that cardioselective BBL do not produce adverse respiratory
effects in patients with asthma or COPD [13,14]. These randomized clinical trials examined only patients with already existing pulmonary
diseases and not healthy subjects. Other studies provide evidence that BBL medication,
even relatively cardioselective agents, produce bronchoconstriction and thereby worsen
respiratory flows in asthmatic patients [10,16]. Our results indicate that the use of BBL medication is associated with a slight
reduction of FEV1 and FVC. Interestingly, the FEV1/FVC ratio was found not to be affected by BBL medication suggesting that the expired
volume, FVC, is lowered in proportion. Indeed, the drug-specific effect of BBL medication
is more pronounced on FVC than on FEV1. This supports the hypothesis that not airway obstruction, but rather restriction
is the more likely mechanism involved in the effect of BBL medication on lung function.
For instance, possible effects on the respiratory muscle strength have to be considered.
It is well established that beta agonists improve the performance of skeletal muscles
[22] and also positively affect respiratory muscle strength [23,24]. The opposite effect by BBL medication is suggested by a recent study from Frankenstein
et al. performed in patients with chronic heart failure [25]. Thus, we hypothesize that BBL medication may result in a slight reduction of expiratory
muscle strength causing a proportional decrease of FEV1 and FVC. However, further studies directly addressing this issue are required.

When reviewing our results, it becomes apparent that from a statistical point of view
both high blood pressure and antihypertensive BBL medication have an effect on lung
function measurements. But the observed lung function differences between exposed
und non-exposed subjects are relatively small, meaning that they have no direct clinical
consequence in healthy individuals. However, we could show that among treated but
not controlled hypertensive subjects FEV1 had a lower volume of 160 mL compared to subjects with no high blood pressure and
no antihypertensive medication. This finding might be of importance on the population
level. One possible explanation for this significant lung function reduction might
be an additive effect of both treatment and persistent high blood pressure. However,
the cross-sectional study design makes it difficult to disentangle the effects of
high blood pressure and antihypertensive medication. Thus, it allows only statements
about a single point in time and does not allow evaluating the effect of long-standing
high blood pressure. Another explanation for this lung function decrement could be
that those with persistent hypertension despite medical treatment have a higher underlying
blood pressure compared to effectively treated subject. Moreover, the effects of high
blood pressure and antihypertensive medication are highly correlated. A detailed analysis
of antihypertensive medication indicates that BBL medication and not any other antihypertensive
medication is associated with a reduced lung function. This negative effect of BBL
medication still remains, when BBL, other antihypertensive medication and high blood
pressure are analysed in the same model. Besides, BBL are the most common prescribed
antihypertensive medication and it has to be considered that BBL medication might
be prescribed for other indications than hypertension, as for example, coronary heart
diseases or heart failure, too. This again suggests that the effect of antihypertensive
BBL medication on lung function is mainly ascribed to the medicament and not to the
indication. Furthermore, a variety of confounders might affect the association between
high blood pressure, antihypertensive medication and lung function. Cigarette smoking
is a common risk factor for both impaired lung function and high blood pressure and
BMI might have an effect on lung function. However, adjustment for these possible
confounders did not influence our results. Moreover, we could show that the association
was not affected by the concomitance of pulmonary diseases and that the negative effect
of BBL medication on lung function is not modified by obstructive lung diseases. This
supports our interpretation that BBL have an effect on lung function in the general
population. Besides, our results suggest that there may be an effect modification
by gender. We could show that in women the percent predicted lung function values
did not differ between subjects with and without high blood pressure. Furthermore,
the multivariable regression analysis revealed a significant interaction between gender
and high blood pressure. This might possibly indicate that high blood pressure has
minor effect on lung function in women compared to men.

The large sample size and the population-based setting are a major strength of this
study. Furthermore, it is one of few investigations differentiating between the effect
of blood pressure and antihypertensive drug treatment on lung function. Nevertheless,
this study has some possible limitation. Methodological bias might lead to insufficient
lung function measurements. Thus in patients with high blood pressure lung function
tests might be stopped earlier, because the respiratory effort might cause an increase
in blood pressure. However, we consider this possible bias unlikely to affect our
findings. Besides, selection bias might limit the representative status of the population
sample included in our analysis. We had to restrict our analysis to subjects aged
40-65 years, because only this age-restricted subset performed lung function tests.
However, as this was a random sample, we consider that our population sample is highly
representative for this age group of the Augsburg population. Moreover, the cross-sectional
study design makes it difficult to make a clear statement about the temporal sequence
and causality between high blood pressure, its treatment and lung function. Several
prospective studies indicated that high blood pressure is a risk factor for reduced
lung function as well as impaired lung function increases the risk for the development
of high blood pressure [7-9,26]. Besides, one has to consider the possible effect of long-standing high blood pressure.
For example, subjects with currently normal blood pressure under medication might
have had high blood pressure for a long time before it was recognized and treated.
Therefore, it is necessary to evaluate the temporal sequence, acute and chronic effects
and the causality between high blood pressure, its medical treatment and lung function
in further prospective studies.

Conclusions

Our findings are in line with previous observations showing an inverse association
between blood pressure and lung function. Furthermore, our analysis indicates that
BBL medication and not any other antihypertensive treatment is associated with reduced
lung function in a general adult population. Thus, our findings may serve as a basis
for experimental testing, as for example by adding measurement of respiratory functions
to outcomes of 'hypertensive' trials.

Competing interests

The authors declare that they have no competing interests.

Authors' contributions

ES was responsible for the data analysis, interpretation of data and manuscript preparation.
JH and ES developed the statistical analysis plan. SK, HS, SG, CM, MH, AP, H-EW, JB,
RMH and JH assisted in the interpretation and critical revision of the results. SK,
HS, CM, MH, H-EW and AP were responsible for the data. All authors read and approved
the final manuscript.

Acknowledgements

We thank all the participants in the study. We are indebted to the KORA study group
which consists of H.-E. Wichmann (speaker), R. Holle, J. John, T. Illig, C. Meisinger,
A. Peters and to all co-workers who are responsible for the design and conduct of
the KORA studies.

Source of Funding

The KORA research platform (KORA, Cooperative Research in the Region of Augsburg)
was initiated and financed by the Helmholtz Zentrum München, German Research Centre
for Environmental Health, which is funded by the German Federal Ministry of Education,
Science, Research and Technology and by the State of Bavaria.

The work was supported by the Competence Network Asthma/COPD funded by the Federal
Ministry of Education and Research (FKZ 01GI0881-0888).